The present invention concerns a proportional valve for a hydraulic dashpot with a piston that slides back and forth on the end of a piston rod in a shock-absorbing cylinder. The piston is provided with pressure-sensitive valves for the exchange of fluid during suction and compression states. The piston separates the cylinder into two compartments. Passages are provided for the fluid that applies pressure to the valves to flow through. Space that communicates with whichever compartment it faces and supplies regulating pressure to the particular shock-absorbing valve is provided on the side of the shock-absorbing valve that faces away from the passages.
Known proportional valves operate in accordance with pilot controls. Pressure against the side of the shock-absorbing valve facing away from the passages controls how far the shock-absorbing valve can be lifted by the main stream in a pressurized space there. Countervailing pressure is for this purpose established in the pressurized space with the aid of system of bypasses. The countervailing pressure does not release the main stream, except for any constant currents through the shock-absorbing valve's disk or at the edge of its associated seat, prior to a specified operating state.
German 4 441 047 C2 discloses a proportional valve of this genus wherein the regulating pressure can also be controlled by a spool accommodated in the bypass system. The only performance curve that can be obtained with this valve, however, in spite of its controls, tends to be degressive (a "degressive performance curve" for short hereinafter), and soft roll-off on the part of the vehicle is, to disadvantage, impossible.
German 3 348 176 C2 discloses a proportional valve that is more remote from the present invention. Its shock-absorbing valve disks are subjected to regulating pressure from a pressure-application compartment 40 by way of a support 38. The regulating pressure is applied through a bypass system that can be opened and closed or choked by an extra sliding valve 45.
There are drawbacks to this valve. The pressure-application compartment is entirely inside the piston and has only one side that can be closed by another support. A series of extra bypass bores extending through the piston and a cutout or bore in the shock-absorbing valve disk complicate the manufacturing process without being necessary for unimpeded access on the part of the volumetric portion needed for the controls.
Another drawback is that the aforesaid valve disk 45 45 combines the function of a shut-off valve with that of a regulating valve. The result is the promotion of discontinuity in the volumetric flow, due for example to flutter on the part of the valve, especially in the event of high-frequency and low-amplitude fluctuations.